A railroad switch point consists of tapered rail sections that are capable of being selectively displaced between two different lateral positions at a rail switch and then locked in the selected position in order to facilitate the desired routing of a train passing through the switch. The two switch points are typically displaced by rods extending from an assembly that is referred to herein as a “switch machine”. Inside the switch machine the rods are usually connected to a motive mechanism which provides reciprocating rectilinear motion controlled by a power unit which is usually placed to one side of the rails.
Such a device is described in Italian Patent No. IT1246656. The device described in that patent operates switch points which are independent, or disconnected, from each other, and it is not applicable to the problem of operating switch points of the interconnected type, i.e. of switch points connected to each other by transverse bars. Switch machines of the interconnected type are shown, for example, in U.S. Pat. Nos. 5,806,809, 6,149,106, and 6,691,958.
The switch machine combines the switch point movement and switch point locking functions into a single mechanism. This reduces mechanical complexity. The switch machine is also enclosed in a weather-proof housing. Also incorporated within the housing are sensors and other electrical control components. The housing and operating assembly are located beneath the switch points and the associated rails.
In such switch machines binding may occur, as described below, when the operating rod does not move along its intended longitudinal line of action. Instead it is subjected to lateral forces tending to cause it to bind at its attachment to the switch point and where the operating rod passes through the switch machine housing. A bearing and a seal are usually provided at the entry point into the housing to align the operating rod and to seal out water and other contaminants. The outer end of each operating rod connects to an associated switch point, and as the operating rod is moved in to and out of the switch machine housing, this substantially longitudinal movement of the operating rod is used to apply force to move the associated switch point laterally. The lateral movement of the switch point requires some change in the angle between the operating rod and the switch point because the switch point is actually pivoting about a pivot point at the other end of the switch point rail section. This change in angle can apply a lateral reactive force on the outer end of the operating rod. This, in turn, causes the inner end of the operating rod to apply substantial lateral force to the bearing and seal mechanism through which the operating rod enters the switch machine housing.
In addition, a more paramount problem that results is due to the thermal expansion of the tongue, or the part that is moved to set the track of the switch. The thermal expansion causes axial motion of the tongue wherein thermal expansion may be more than an inch depending on the temperature and length of the tongue. This lateral reactive force can cause premature failure of the seal and binding of the operating rod relative to the housing, which can cause the switch machine to lock up.
The switch assembly in the prior art requires grease at certain locations to insure smooth operation of the moving parts. Towards this end, regularly scheduled maintenance of the switch assembly must be accomplished to insure that all parts have sufficient grease.